Tomato Alternaria blight is a disease caused by the fungus Alternatio solani Sorauer. Greenhouse owners and residents of regions where hot weather gives way to rain are especially likely to encounter this pathogenic microorganism. How to identify and prevent a dangerous disease?
Description
Alternaria blight is one of the main tomato diseases, which is also called dry or brown spotting. It was first discovered at the beginning of the 20th century in the Kursk region. Today, the fungus affects tomatoes in the southern and central parts of Russia, as well as countries located in the southwest - Ukraine, Moldova. The average crop damage is 50%, and under the worst conditions even 100%.
The progression of the disease is indicated by small brown spots that appear first on the lower and then on the upper part of the plant.
The spots on the leaves are round, and on the stem they are elongated. Under the influence of dampness, the ulcers become covered with a barely noticeable black coating and slowly grow, merging into one large area.
The fungus affects not only large parts of the plant, but also peduncles and sepals, a significant part of which is gradually covered with small round black spots. Due to extensive tissue necrosis, dry leaves fall off, and the damaged part of the stem often breaks, resulting in the death of the plant.
A tomato affected by Alternaria blight is covered with depressed spots with a black coating. Most often, ulcers on fruits are located around the stalk or in places where the skin is damaged. The fungus also attacks the core, causing the tomato seeds to turn black and lose their viability. Affected fruits ripen prematurely or fall off.
Causes
Just like all fungi, the Alternatio solani Sorauer mushroom actively develops in conditions of high air humidity. Such conditions are created when summer days with temperatures of +24–+30 ⁰С give way to night rains. In closed ground, the main catalysts for the development of pathogenic microflora are excessive watering and poor ventilation. Under such conditions, the incubation period for the development of the disease is 3–4 days. The yield of plants affected by Alternaria is reduced by 20–50%.
Alternaria also develops on plants with mechanical damage. Conidia and mycelium that have entered the soil from an infected plant provoke diseases of tomatoes and other nightshade crops.
The fungus develops especially often in film greenhouses and greenhouses on early-ripening tomatoes with high air humidity.
How to prevent and cure?
As you know, treating fungal diseases is a very difficult process. Therefore, in order to save yourself from headaches about the harvest, it is better to try to prevent the development of pathogenic microflora. To reduce the likelihood of tomatoes becoming infected with Alternaria, do the following:
- After the end of fruiting, the bed is cleaned of plant debris, and the soil is thoroughly plowed.
- In greenhouses, where tomatoes grow in the same place several years, before sowing, treat the soil with a solution of potassium permanganate, copper sulfate or other disinfectant.
- Water the plants at the roots.
- Medium-growing and tall varieties are tied up, and the leaves at the bottom of the plant are removed.
- Alternate planting tomatoes with other plants. The crop is planted in the same place 3 years after the previous time.
- Mixtures containing large amounts of potassium are used as fertilizers.
- Select varieties with high immunity for planting. The Sanka, Lyana, Golden Bullet, and Luch varieties are endowed with good immunity to Alternaria blight. Among the tomatoes of hybrid origin, the seeds of Alex, Nadezhda, and Aurora are planted.
- Use disinfected healthy seeds for sowing.
- At intervals of 2 weeks, tomato bushes are treated with fungicides. The number of sprays should not exceed 3–4.
Please note that for planting you cannot choose a place where eggplants, potatoes and other nightshade crops grew last season, since they are susceptible to the same diseases, including Alternaria.
Treatment of tomatoes begins immediately after the first signs of the disease are detected with contact fungicides. Such drugs include Antrakol 70 WG, Ridomil Gold MC, Ditan M-45, Quadris. When choosing a treatment product, you need to take into account the fact that not all preparations that contain copper are suitable for the treatment of dry spotting.
Before purchasing a fungicide, you should carefully read the instructions.
In addition to pesticides, biological preparations Fitosporin and Trichodermin are used for treatment. In case of untimely treatment or its absence, the affected tomatoes die, and the fungus enters the soil and spreads to neighboring plants.
If you take preventive measures and treat diseased plants in a timely manner, the harvest can be saved. The main rule for healthy plants in a greenhouse is the correct watering and ventilation regime. Only those gardeners who comply with agrotechnological requirements will be able to avoid crop loss.
